Field of the Invention
The present invention relates to a three-dimensional shape measuring apparatus that measures a three-dimensional shape of a specimen on the basis of a microscope image.
Description of the Related Art
It is important to measure three-dimensional shapes of micro components or areas in order to reduce the size of an industrial product and to sophisticate the industrial product. In order to manage the quality of electronic components or materials, the geometric shapes of the surfaces of the electronic components are measured, and the geometric shapes are quantified.
As a method for measuring the geometric shape of the surface of a specimen such as a component, a method using a stylus-type surface roughness measuring machine has been used. In this method, the shape of an object to be measured is measured by precisely tracing the surface of the object to be measured by using the tip of a mechanical stylus, and therefore highly reliable data can be obtained.
Meanwhile, non-contact measuring machines using various measurement principles have been widely used. By using the non-contact measuring machines, an object to be measured can be easily measured without being damaged, and therefore the non-contact measuring machines have been spread rapidly in recent years. Many of the non-contact measuring machines use an optical technique. A representative example of a commercially available non-contact measuring machine is confocal microscopy.
A basic principle of measurement by using confocal microscopy is described below.
As the confocal microscopy, a laser scanning confocal microscope described in Japanese Patent No. 3847422 is publicly known.
A laser scanning microscope two-dimensionally scans a specimen with a laser beam that has been condensed in a spot shape by using an objective, and the laser scanning microscope receives reflected light via a confocal diaphragm that is arranged in a position conjugate to a focal position of the objective. The confocal diaphragm only receives light of a focused portion, and therefore only the focused portion is imaged. The obtained image has a smaller depth of focus than that of a normal optical microscope, and the obtained image is generally referred to as a confocal image.
A small depth of focus is used to measure the surface shape of a specimen in confocal microscopy. Namely, a plurality of confocal images having a small depth of focus are captured while a relative distance between an objective and the specimen is being changed. By obtaining a position in a Z-axis direction that provides a maximum luminance in each pixel position of an image, namely, a focusing position, the surface shape of the entirety of the specimen is measured.
FIG. 8 illustrates a curve called an I-Z curve. The I-Z curve indicates a relationship between a relative distance Z between an objective and a specimen and an intensity I of light reflected by the specimen. As illustrated by the I-Z curve of FIG. 8, when a focal position of the objective matches a surface position of the specimen, light has the largest intensity.
In Japanese Laid-Open Patent Publication No. 2004-020433, for example, a method for obtaining a focusing position in each of the pixel positions from the plurality of confocal images above has been proposed. In this method, an intensity I of light reflected from a specimen with respect to a relative distance Z between an objective and the specimen is obtained in each discrete position in such a way that a measurement accuracy and a measurement time are not an exchange condition, an I-Z curve approximate curve is formed, and a surface position of the specimen is estimated.